Electro-magnetic distance measuring device



2 Shee ts-Shee t 1 J. A. GREGORE ET AL ELECTRO-MAGNETIC DISTANCE?| MEASURING DEVICE Jan. 22, 1957 Filed .July s, 195o J. A. GREGOIRE ET AL Jan. z2, 1957 ELECTRO-MAGNETIC DISTANCE MEASURING DEVICE Filed July 3, 1950 2 Sheets-Sheet 2 ALM) limited States ELECTRO-MAGNETIC DISTANCE MEASURING DEVICE Application July 3, 1950, Serial No. 171,944 Claims priority, application France July 7, 19449 3 Claims. (Cl. 343-12) The present invention relates to a radio system for measuring the distance between two radio stations `by means of phase displacements of a non-pulsatory electromagnetic wave.

Telemetric systems are known in which distance is measured by the time required to transmit a radio signal from a local station to a remote station and an answering signal to return. In these systems an audio frequency wave of precisely known frequency and phase is modulated onto a first high frequency wave carrier, then transmitted from the local station toward the remote station, there received, demodulated and modulated onto a second high frequency wave carrier and retransmitted, unaltered in frequency and with constant phase-shift backward to the local station. The measurement then consists in determining by means of a phase comparison circuit the total phase delayof the audio frequency signal for the to and fro path, taking into account the known parasitic phase delay introduced by the transfer of the modulation from the first carrier to the second carrier made at the remote station generally termed responden In these systems an audio frequency signal generating means is necessary.

In some other known systems a high frequency closed radio-electric path is used which is energized by audio frequency feedback for such a modulation frequency that the total phase delayfof the circuit will be an integer multiple of a cycle. In other words, a signal of variable known frequency is modulated onto the outgoing carrier wave and the return signal is demodulated from the '45 returning carrier wave and then constitutes the input arent signal which is modulated onto the outgoing carrier Wave. 2

The knowledge of the frequency for which the closed,

path becomes self oscillating gives the distance.

In these other known systems an audio frequency sigy nal generating means is unnecessary. These other known systems are however subject to disadvantagesas follows:

The operation is carried out at variable frequencies since the modulation frequency for which the closed path becomes self oscillating is variable with the distance.

Since the parasitic phase delay in the remote station also varies according to the frequency, one is obliged to introduce corrections of a dubious accuracy. Moreover measurement of a variable distance is transformed from the measurement of a phase change `to the measurement of a variable audio frequency. The range of distances measurable with the device is thus restricted by the bandwidth necessary for the radio frequency transmitters and receivers of the local and remote stations.

The object of the present invention instead is a measuring device using as oscillatory circuit the to-and-fro path between the local and the remote station and operating on a single constant audio frequency, in spite of variationV of the distance to be measured.

tance is carried out by means of a closed radio-link or loop including a phase shifter the phase delay of which is controlled by the discrepancy between the instantaneous arrests? atented Jan. 22?, 1957 the `angular shift of a rotor with respect to a referencel position. 'The rotor will thus supply an angular shaft position proportional to the distance to be measured, which can then be easilyintroduced into any operative computor.

The invention will be described hereunder in detail, with reference to the accompanying drawings in which:

Fig.` 1 is a schematic diagram of one embodiment of the invention showing in block form the components of the circuits at the local and remote stations between which the distance is to be measured; and

Fig. 2 is a schematic diagram showing in greater detail certain of the components of a modified form of the invention at the local station.

Referring to Fig. l, at station A an oscillator 1 generates a high frequency carrier designated by F1.` 2 is a modulator which is fed by the carrier F1 and by an audio frequency sine wave signal designated by fa and coming :from the phase shifter 15. The modulator Z combines the modulating signal fa with the carrier in the well known manner and the resultant compound wave is fed to a radio frequency transmitter 3 and then transmitted to mobile station M through antenna 4. The transmission path is indicated by dashed line 5 connecting station A with station M and the modulated signal transmitted over -this path is indicated by thesymbol Fi/fa.

At station M .is located a responder 6 comprising a receiver 37 and a transmitter 38. Receiver 37 demodulates the signal received through antenna 7, and the de modulated signal fa -is applied, through connection 39, to transmitter 38. Transmitter 33 retransmits, through antenna `8, the -signal fe. over a different carrier wave F2. The transmission path is indicated by dashed line 9 connecting station M -to station A and the modulated siglnal transmitted over this path is indicated by the symbol FZ/fa.

Responder 6 is not disclosed in detail since such devices are known, for example from U. S. Patent 2,248,727 of July 8, 1 941 issued to Howard M. Strobel.

vAt station A, the compound wave Fz/fa is received, through antenna 10, in 'a receiver 11 and demodulated by a detector 12 to obtain the original modulating signal fa. This signal is then increased in strength by an amplier 13 and next applied to a filter 20 and toA a phase correcting device 14.

'The' output signal from phase corrector 14 is designatedV on Fig. l 'by the .same symbol fa, as the input signal to' modulator 2 and has the same vfrequency as the latter but has undergone a substantial phase shift.

The closing between phase corrector 14 and modulator 2 "of the audio frequency loop which connects the local and remote sections A and M is effected, through a phase shifter 15, the mechanical shaft 19 of which is driven by a motor 16. Motor 16 is energized by a follow-up cont-rol unit comprising a frequency discriminator 17 and amplifier 18. Discriminator 17 supplies a voltage proportional to the difference between the instantaneous self-oscillation frequency of the looped trans- "mission path (the frequency for which the total phase 2xt-il C over a certain natural audio-.requencyf ,for wh wherein c is the light velocity and d the double of, the distan@ to be' measured), itc. the ,phaseeerfeetmardef. Vies. 14,. and .that a'arestieellvl intrdiieed liv#-the!filleuls.-y mitters 'i the receivers, thezaniplifiers'andthefnjiodlll akidl.; I.

equal delay die to the phase-.shifter is, @sa vifhehy the' fetal .phase delay previeuslr referred cornes equalto a multipleufof` acyclff` 'Vfrequency fg,

TherhaSe-Shift etphas een a vaine equalend -Qppslte Ete Vthe.-'Pleresitle. @has valuebf the'v toV and vfro transmission' 'v1atl 1. i phasefshifw. dueto phesershfter l5 isv give eqiiati-onz' 'k i. l,

. "I so a+-2 2@ wherein k is an integer.

lIf the distance!!v `varies and becorries d., they self-:oscilf latyQnzfreqilency of 'tlieM-to, and fro transmission .path tends to depart from fa and/to take on a valueff givenassuming that phase-shifter 1'5 is of a type the phase-slhi`ft 0f. thi-ah.iaiadependentef the frequency. Phase-Shifter 15 is moved Ibyfthefollowup controlunit `untill it carriesA toa new angular position, andV introduces aphas'e delay.

l fa

In this new angular position, the output voltage of dis-v efirnaatef. ..17 is' .zere and rector it6 'remeirisiL't/rest- 5o The to and 'fro path thus oscillates on afned audiof fregpegy @and filter. 2.0 may be,.used et theeutput of' ampler'fl. S0' es te insiire .hat thee'seillatens. tarfeieref..

cisely produ at the frequ 'A )friend not atsc'iniefotlzier;`

euli. freaueeeles". hei/iria, willie. afdiifefeneeeeeel 1.9

kc e

The distance d is indicated. directly and continuously by the positionof the pointer`21 (coupledimecihanically with thegshaft 1 9), 0 1; lire, scale of. the distance .indicator'22.' i Y the nlsasershifter 1.5. ie Such, that it eneurestthe teler. fiOnShP.. 6:@ betwee1i-t1egmeehaaiea1 retteii 0..Qf`..'i.ts.. shaft 1Q andf the-electric phase delay :p which it intro,- duc'es, the neutralisation of lthetp'arasitic phase-shift dile tothe electric' cir-cuits'in stations A 'and Mrnay be effected by.- givingto the-shaft il9-anfangular p'osition'which is equal'and `oppositeuto the parasitic phase-shift-for the zero phase-shiftintroduced 'by 15, i'. e. when f V70 is almultiple of alcycle.`

tuned to fa, receiving audio energy from amplifier 13 of Fig. l, 23 is an amplifier and 24 a conventional frequency discriminator. The `output signal of said discriminator is detected by rectifier bridge 25 land rectified voltage is applied to servo-motor 16 through leads 26 A 'sine wave voltage of frequency fa is also applied `to the primary winding of transformer 2S. Via an -attenuatingy circuit-.31 'andf a -90'95 advance'iphaseshifter circuit 32,-the'secondary windings of thisVt'ransforiier feed selsyn windings 29 and 30 'respectively with volta-ges Idisplaced with respect to each other by A rotating field is thus,obtainedinaselsyn 33. n v w The. rotor winding 35i of .selsyn 33 is -mounted upon shaft 19 ofmotorel' and' itsoutpucterminals are connected to input terminals of modulator 2 through leads 35 and 36.

i Restiposition of rotor 34 being shifted by angle 0a in orderto'compensa-te the parasitic phaseishi-ft we'have:4

assuming liv-#1, which 'isread on scale 2,2. directly bJatedin-,terms of distance.l l Y. .t

.what -we claim is;`

lfqA systemfor measuring the distance.. between a yfirst point and, aysecond :pointcomprisingyat -saidfrst point.- alst. radio. frequencytransmitter. having a modulation parlisandadapted to. transmit a first amplitude-modulated signa1..aV variable.. phase-shifter,l having its: output coupled tn the modulationrpart. of said rst transmitter, a first2 radio frequency .receiver at. said second pointfor receivingandfdernodulating saidarstisignal, connection means forL applying. said dem-odulated` first. signal. to a 'second transmittenat said second point, .said second transmitter.' retransrnitting` toward sadirstwpoint a second :signale anlplitudefmodulatedi by; the .same ifrequency. as= the; first' signaLrasecond.radio frequency receiver atthe :first point foirrderiving .thel modulation component of rsaid second signal, connection means lbetween the second receiver. andrthe input fof, the;v variablez-.phase-shifter for applying theginodulation compomentof said. second ,signalrto-saids variable.;.phase.shifter,'fwherebyr the. whole. closed pathinclkuding the first' transmitter, thettransmission-path be. Tweenzthe first: transmitter ands-the frstareceivenwthe connection. means 'between the firstreceiver andthe. sec.- v ondi transmitter, thentransmission. path between thesssecL ond-t1 transmitter .and the. secondJreceiver and .the phaseshifter. insented; between .the second:receivertand:the firsttransmtter.: tends .f to; self-.'scillate on' a .modulation ifre quency forfwhichitsstotal v phase-.shifcris .anrintegnaly mul.- tiple; o ancycle:for;.a;given.distance betweemthe first and'irecond. points', -and;a.follow:.up. unitadapted. to.'- controltfthe. phasezshiften; and. comprising. a-..freqi.iency;` dis-,1 criaitnationsv means havingzits inputlrconnectedwtocthe; in- PUi "of .L the; 1 phaseeshifter', said frequencyndiscrimiriaton.: v means-.being tunedl togaargiven fixed freqtuencyf.and.givingV atyits output avoltage proportional. to.;l thezdiiference fbef. tweeriztheA frequency at which .thewhole closedpathi:tendsto .'--self-,osillate and t. the given. :fixed frequency to. z which: Said. frequency zdiscrirninationlisytuned, Tand r a .motori dniv. t ingrth;.Yariab1espl1aseshifter. andiafed byiasaid. voltage, Whnrebis therr selfeoscillation frequency. .of the. whole, path: is.}cQ`In-P1lei tto, be; 4equal-.tov` theftuning freqiiencytofI the. I d-iserirnination.meansl .w y w l 2. A system for measuring the distance. between; two, Staiinf. Said... System, comprising at one. of saidzzstations: a ,first modulated: radio.;transmitter operating'on. 'a first car-.rien frequencyg a..is.econd1 radio reccivortuned: to a Samedi-Carrier; frequency, awvariable.- phasefshiftensand', a., frequency discriminator having their. signal inputsv cou-- pled/:..tofthea Outputofasaid, second' receiver,n anlnazseltvomeshaalern.i^ef 11ri1e-dl between. the, outputeoffsaid discrimif.`A Daten-a .er-plies shiftfA varying; elements; oie-said; phase; Shften the. `Signal.output of saisit phase. shifter bein-geene@ calipled 'to the modulation input of said trst transmitter; said system comprising at the other of said stations: a first radio receiverv tunedlto said rst carrier frequency, a second modulated radio transmitter tuned to isaid second carrier frequency, and means coupling the output f said rst receiver `to the modulation input of said ysecond transmitter. y

`3. A system' for measuring the distance between two stations comprising at each of said stations a modulated radio transmitter and a radio receiver, said transmit-ters being tuned t-o different carrier frequencies and the receiver a-t each station being tuned to 'the carrier frequency of the transmitter lat the other of said stations, -and means providing `at each of said ystations a signal path for modulation frequencies between the output of .the receiver at that station and the modulation input of the transmitter at that station, the coupling at one of said stations including a variable phase shifter, .said phase shifter having a signal input for modulation frequencies coupled to the output of the receiver at said one station, whereby the closed loop including both transmitters and receivers and the paths between sa-id two stations tends to self-oscillate with a modulation on the carrier Waves between `said stations for which the totalphase change around the loop is an integral number of cycles, a frequency discriminator having its signal input lcoupled -to the output of the receiver at vsaid one of said stations, and `a servomecha- References Cited in the file of this patent UNITED STATES PATENTS 1,750,668 Green Mar. 18, 1930 2,424,263 Woodyard July 22, 1947 2,528,119 Crosby Oct. 31, 1950 2,529,510 Manley -..1 Nov. 14, 1950 2,537,574 Crosby Jan. 9, 1951 2,542,983 Beatty Feb. 27, 1951 2,546,973 Chatterjea Apr. 3, 1951 FOREIGN PATENTS 103,682 Sweden Feb. l0, 1942 OTHER REFERENCES Radio Engineering by Terman, 3rd edi-tion, McGraw- Hill, pages 483-501 and 522-525. 

